Silk Spinning Mechanics Decoded by Georgetown Physicists

"Having a deeper fundamental understanding of the [silk] spinning process provides a starting point for those interested in creating smarter bio-compatible materials," says Daniel Blair, assistant professor of physics at Georgetown.

February 16, 2012– A new understanding of the way spiders and silkworms create silk, discovered by two Georgetown physics professors and a collaborator, will help advance artificial silk-making for bone grafts and other uses.

Working with Chris Holland of Oxford University, Georgetown physicists Daniel Blair and Jeffrey Urbach have found that silk fiber formation might be much simpler than expected.

The scientists’ work will be published in the March 8 issue of the scientific journal Soft Matter.

Smarter Materials

Prior to the Georgetown-Oxford study, the prevailing view of how silk is made included biochemistry.

“Because of its versatility, flexibility and strength, silk is used for everyday materials like linens and clothes, but silk can also be used by the biomedical community to create skin grafts, tissue scaffolds and other therapeutic materials.” Blair adds. “Having a deeper fundamental understanding of the spinning process provides a starting point for those interested in creating smarter bio-compatible materials.”

The Air Force Office of Scientific Research (AFOSR) funded the professors’ research.

Shear Genius

Using a laser microscope and a shearing device called a rheometer, scientists mimicked the creation of silk, upper right, by the mori silkworm, bottom left. Reproduced from C. Holland, J. S. Urbach and D. L. Blair, Soft Matter, 2012, 8, 2590-2594 (DOI: 10.1039/C2SM06886A) by permission of The Royal Society of Chemistry.

Shearing is the technical term for the act of putting material between two surfaces and displacing one of those surfaces relative to the other.

“It’s similar to the action of moving the top of a book relative to the bottom,” Blair says. “In this case, the insects shear a protein solution as it travels down their spinning duct to the spinnerets, which turns the liquid into thread.”

Before this study, it was unclear whether the shearing action itself was sufficient to create the thread without biochemical modification.

“For a long time, people have been trying to establish at least some understanding of silk production,” explains Blair. “One of the big questions has been – how does that process happen?”

Direct Observation

Using a special laser microscope and a precision shearing device known as a rheometer, the researchers were able to mimic the shearing motion by applying force to native silk protein material from dissected silkworms.

The device then allowed them to directly observe the action of the threads being made, which provided evidence that the shearing action alone was sufficient to make silk.

“This is the first time anybody’s visualized native silk protein – that is, protein that’s come directly out of the bug – producing fibers,” Blair notes.

What’s Next?

Blair says the research is fundamental to the understanding of the insects and for future applications.

“In order to man-make silk, you first have to understand how the bug creates it,” he says. “We’ve used biologically produced materials such as silk threads for millennia, but if materials physics hopes to unlock what biology has perfected, we will need to develop a whole new set of tools and techniques.”